If using presta tubes in Schreader drilled rims, either get one of the stepped nuts shorn above, OR get a presta-schreader grommet to take up the excess space, OR find a washer that fits the outer diameter of the presta stem and put it between the tube and the rim and snug down the nut on the outside, OR put two nuts on the stem - one on the inside of the rim and one on the outside and snug them together.
I am happy to hear people have had good luck just using presta in a schreader hole without issue, but that has not been my experience - the tube sees a lot of extra stress trying to push itself through the hole and this often causes flats.